The present invention relates generally to the field of waveguides. In particular, the present invention relates to photodefinable silsesquioxane compositions that are useful as optical waveguides.
Light is becoming increasingly important in the transmission of data and communications. For example, fiber optic cables have replaced conventional electrical cables in a number of applications. Guides and switches are needed to capture, carry and distribute light carrying such transmissions.
Optical waveguides may be used individually or as an array supported on a substrate. Such waveguides typically include a core material and a cladding layer. Light propagates in the core material and is contained by the cladding layer which has a lower index of refraction than the core material. Planar optical waveguides are designed to transmit optical radiation across a two-dimensional substrate surface. This device usually performs a passive function on the optical radiation so as to modify the output signal from the input signal in a particular way. For example, splitters divide an optical signal in one waveguide into two or more waveguides. Couplers add an optical signal from two or more waveguides into a smaller number of waveguides. Spectral filters, polarizers and isolators may be incorporated into the waveguide design. Wavelength division multiplexing (xe2x80x9cWDMxe2x80x9d) structures separate an input optical signal into spectrally discrete output waveguides, usually by employing either phase array designs or gratings. Planar optical waveguides are particularly advantageous in that they may include multiple functions on one platform.
Waveguides may also contain active functionality, i.e. where the input signal is altered by interaction with a second optical or electrical signal. Exemplary active functionality include amplification and switching such as with electro-optic, thermo-optic or acousto-optic devices.
A number of structures suitable for use as optical waveguides are known, particularly those prepared from siloxanes or silsesquioxanes. For examples, WO 97/24223 (Risen et al.) discloses the use of highly-carboxylated polysiloxanes. Such materials, when they contain methyl or vinyl side groups, can be photolytically cross-linked in the presence of a free radical photoinitiator to form insoluble siloxane films or patterns. The uncross-linked materials can then be removed with an organic solvent. The remaining cross-linked material is then thermally oxidized to form a patterned silica film which is useful as an optical waveguide.
U.S. Pat. No. 6,144,795 (Dawes et al.) discloses a method for forming planar optical waveguide cores using either a transfer printing technique or an embossing technique. Such waveguides having at least one of the core and cladding materials being an inorganic-organic hybrid including an extended matrix containing silicon and oxygen atoms with at least a fraction of the silicon atoms being directly bonded to substituted or unsubstituted hydrocarbon moieties. The hydrocarbon moieties can be either alkyl or aryl. Methyl and phenyl are the only hydrocarbon moieties specifically disclosed.
U.S. Pat. No. 6,087,064 (Lin et al.) discloses certain silsesquioxane polymers useful in photoresist compositions. The photoresist compositions include a polymer blend having 30 to 90 wt % of a silsesquioxane polymer of the formula (R1SiO1.5)nxe2x80x94(R2SiO5)m, wherein n and m are greater than zero, R1 is hydroxyphenylalkyl having at least 2 carbon atoms in the alkyl moiety and R2 is selected form the group consisting of alkyl, cycloalkyl, and aryl; and 70 to 10 wt % of a non-silsesquioxane polymer. Neither waveguides nor methods of manufacturing waveguides are disclosed in this patent.
Known methods of manufacturing waveguides include 1) manually placing glass fibers into hollowed out areas on a substrate, 2) filling a mold of a desired structure with a polymeric material that is thermally cured and later removed from the mold, and 3) depositing a bulk waveguide material on a substrate, coating the bulk material with a photoresist, imaging the photoresist, and removing the undesired bulk material by etching and then removing the photoresist. Each of these processes has drawbacks, such as requiring multiple steps to define the waveguide, potential sidewall roughness issues, limited resolution and increased labor costs.
There is thus a need for methods of manufacturing waveguides that require fewer steps than conventional processes, have better resolution and less sidewall roughness.
It has been surprisingly found that waveguides can be easily prepared by the lithographic methods of the present invention. A variety of waveguide structures can be prepared by the present invention.
In one aspect, the present invention provides a photodefinable composition including a silsesquioxane oligomer including as polymerized units a monomer of the formula (RSiO1.5) wherein R is selected from hydroxyphenyl or hydroxybenzyl; and a photoactive component, wherein the solubility of the silsesquioxane oligomer is altered upon exposure to actinic radiation.
In a second aspect, the present invention provides a method of manufacturing an optical waveguide including the steps of: a) depositing on a substrate a layer of a photodefinable composition including a silsesquioxane oligomer including as polymerized units a monomer of the formula (RSiO1.5) wherein R is selected from hydroxyphenyl or hydroxyphenyl(C1-C5)alkyl; and a photoactive component; and b) exposing the composition to actinic radiation to form an optical waveguide.
In a third aspect, the present invention provides an optical waveguide including a core and a cladding, wherein at least one of the core and cladding includes a silsesquioxane polymer including as polymerized units a monomer of the formula (RSiO1.5) wherein R is selected from hydroxyphenyl or hydroxyphenyl(C1-C5)alkyl.
In a fourth aspect, the present invention provides an electronic device including one or more waveguides including a core and a cladding, wherein at least one of the core and cladding includes a silsesquioxane polymer including as polymerized units a monomer of the formula (RSiO1.5) wherein R is selected from hydroxyphenyl or hydroxyphenyl(C1-C5)alkyl.
In a fifth aspect, the present invention provides a photodefinable composition including a silsesquioxane oligomer including as polymerized units a monomer of the formula (RSiO1.5) wherein R is selected from hydroxyphenyl or hydroxybenzyl; one or more organic cross-linking agents; and a photoactive component, wherein the solubility of the silsesquioxane oligomer is altered upon exposure to actinic radiation.
In a sixth aspect, the present invention provides a method of manufacturing an optical waveguide including the steps of: a) depositing on a substrate a layer of a photodefinable composition including a silsesquioxane oligomer including as polymerized units a monomer of the formula (RSiO1.5) wherein R is selected from hydroxyphenyl or hydroxybenzyl; one or more cross-linking agents; and a photoactive component; and b) exposing the composition to actinic radiation to form an optical waveguide.
In a seventh aspect, the present invention provides an optical waveguide including a core and a cladding, wherein at least one of the core and cladding includes a silsesquioxane polymer including as polymerized units a monomer of the formula (RSiO1.5) wherein R is selected from hydroxyphenyl or hydroxybenzyl; and one or more organic cross-linking agents.
In an eighth aspect, the present invention provides an electronic device including one or more waveguides including a core and a cladding, wherein at least one of the core and cladding includes a silsesquioxane polymer including as polymerized units a monomer of the formula (RSiO1.5) wherein R is selected from hydroxyphenyl or hydroxybenzyl; and one or more organic cross-linking agents.